1. Field of the Invention
This invention relates to a diecast machine to mold a molded product having an amorphous phase and to a diecast method.
2. Description of the Related Art
It has been previously known that even in the case that a specific group of alloys is subjected to cooling at the cooling rate equal to or less than 100° C./s, the specific group of alloys make glass transition to become an amorphous metal material (metal glass) (for example, “Monthly Functional Material” CMC Publication, June/2002, Vol. 22, No. 6, pp. 5–9). The metal glass possesses amorphous properties such as high strength, low Young's modulus and high elastic limit, and it is expected that the metal glass is used widely as structural members.
As manufacturing methods of the metal glass, a water quenching method, an arc melting method, a permanent mold casting method, a high-pressure injection molding method, a vacuum casting method, a die locking casting method, a spinning disc reel method and the like can be cited. Moreover, it is known that the large shaped metal glass (bulk metal glass) can be manufactured by use of these methods (“Monthly Functional Material” CMC Publication, June/2002, Vol. 22, No. 6, pp. 26–31).
As described above, it is expected that the metal glass is used widely as the structural members and the structural members take generally complex shapes including concave or convex shapes in many cases. In the methods mentioned above, there has been a case that the metal material is not molded into the complex shape, and that the metal material did not become amorphous even when the metal material is molded into the complex shape.
Meanwhile, as a method of molding the metal material into the complex shape, a high-pressure die casting method which is generally used in molding a light metal is known. In addition, the high-pressure diecasting method is classified into a horizontal high-pressure diecasting method and a vertical (perpendicular) high-pressure diecasting method depending on injection direction of the heated metal material (melt).
Specifically, the horizontal high-pressure diecasting method can control the height of the diecast machine to be low, the structure of the diecast machine is simple and the diecast machine causes few damages. Therefore, the horizontal high-pressure diecasting method has become the mainstream of the high-pressure diecasting method which molds the light metal. Incidentally, in the horizontal high-pressure diecasting method, when an atmosphere within a sleeve is the air atmosphere, air (atmosphere) tends to be involved in injecting the melt (metal material). Therefore in general, the melt is injected after the air within the sleeve is exhausted by use of an air vent or a vacuum evacuation system. Moreover, in the horizontal high-pressure diecasting method, it is also performed that the air within the sleeve is exhausted by moving a plunger at low speed and the melt is injected by moving the plunger at high speed after filling the sleeve with the melt (metal material) (for example, Itsuo Ohnaka, one other “Melt-processibility” Corona Publishing, September/1987, pp 119–120).
On the other hand, in the vertical high-pressure diecasting method, a contact area of the melt (metal material) and the sleeve and a contact area of the melt and the air (atmosphere) within the sleeve are small. Therefore, according to the vertical high-pressure diecasting method it is easy to mold the thin-walled molded product with fine surface properties.
As a representative example of the vertical high-pressure diecasting method, a squeeze diecasting method to solidify the melt while applying a high-pressure of 50 MPa to 200 MPa on the melt can be cited. The squeeze diecasting method can mold the thin-walled molded product with fine surface properties, but can only mold a simple molded product taking a shape to allow pressure to be applied on the entire melt. Moreover, since high-pressure is applied in the squeeze diecasting method, a metal mold tends to be damaged. Therefore the squeeze diecasting method is used only for the case of molding special molded products (for example, Itsuo Ohnaka, one other, “Melt-processibility” Corona Publishing, September/1987, pp 120–122).
Furthermore, a method (vacuum die casting method) has also been proposed, which prevents oxidation of the metal material at the time of applying heat on the metal material by creating vacuum inside the housing while covering surroundings of heater heating the metal material (Zr—Cu—Ni—Be), sleeves and the like with the housing (for example, Japanese Patent Laid-open No. 1999-156517).
However, according to the prior art mentioned above (the horizontal diecasting method, the vertical diecasting method and the vacuum diecasting method), there has been the case that when the melt (metal material) is poured from a melting furnace into the sleeve, temperature of the melt is decreased and a heterogeneous nucleation is generated. In other words, according to the prior art mentioned above, it has been difficult to increase a ratio of the amorphous phase contained in the molded product due to incorporating crystals into the molded product.
Moreover, in order to melt metal material, a high-frequency induction coil, which is efficient at heating, is generally used as a heater to heat the metal material. However, in the above-mentioned vacuum diecasting method, unless the degree of vacuum inside a housing is extremely increased, when the metal material in the housing is heated with the high-frequency induction coil, corona discharge occurs. Therefore, there was no other choice but to use an electric furnace or the like, which has a heating efficiency lower than that of the high-frequency induction coil.